This invention relates generally to refrigeration systems for household refrigerators and freezers, and more particularly to such systems employing a subcooling flow control valve to control flow of refrigerant between the condenser and evaporator for maximum energy efficiency.
Household refrigerators and freezers nave been the subject of increasingly strict legal regulations regarding the energy efficiency of these units, and this has required the extensive redesign of these units to meet these regulations. While some of the improvement in efficiency has been obtained by improvements in the cabinet insulation, it has been found that the greatest improvement can be had in the refrigeration system itself. Considerable increases in efficiency have been made in the compressors as well as the sizing of the condensers and evaporators, but the latter tend to provide a peak efficiency at one certain set of operating conditions, such as ambient temperature, door openings, and type and size of the contents stored in the unit.
Recently it has been found that further increases in efficiency can be obtained by the addition of a subcooling flow control valve positioned between the outlet of the condenser and the inlet to the capillary tube that provides the necessary restriction and pressure drop at the entrance to the evaporator. The flow control valve functions in two ways to increase efficiency of the system. First, when the compressor is running, the valve operates in a modulating manner to allow only subcooled liquid to enter the capillary and thereby prevent any vapor from entering. Second, when the compressor stops, the valve closes to prevent any refrigerant from flowing in either direction while the compressor is not running, and the valve then must quickly reopen when the compressor restarts.
The valve is operated by a sealed capsule of a saturated refrigerant which expands and contracts in response to the amount of subcooling of the refrigerant leaving the condenser and entering the capillary tube to insure that only subcooled liquid refrigerant enters the capillary. If the temperature of the refrigerant rises above a predetermined point set below the saturation temperature, the valve closes to prevent flow in either direction between the condenser and the capillary. Such a system and valve has been disclosed in the copending patent application of J. D. Powlas, Ser. No. 671,390, filed Mar. 19, 1991, and assigned to the assignee of the present application. However, that system and valve have been found sometimes to operate in a somewhat unstable manner under certain conditions and the valve has been somewhat slow to open and close when the compressor is started and stopped. Furthermore, it has been observed that sometimes the valve has reopened after the initial closing after the compressor has stopped. If the valve reopens, the pressure equalizes across the valve and there is a significant loss of system energy efficiency. Thus it is desirable to insure a rapid response to opening and closing conditions and to insure that the valve will remain closed while the compressor is off.